1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus which is arranged to handle a plurality of kinds of image signals corresponding to different aspect ratios.
2. Description of the Related Art
In recent years, television sets or monitor displays having wide display screens have been proposed, and not only television sets or monitor displays having a conventional aspect ratio of 4:3 but also those having a wide-screen aspect ratio of 16:9 have been commercially available. In general, wide-screen television sets are arranged so that users can select a substantial display screen size corresponding to either of the 4:3 and 16:9 aspect ratios. Accordingly, the wide-screen television sets can cope with an image signal having either of the 4:3 and 16:9 aspect ratios.
An image recording and reproducing system suitable for use in such a wide-screen monitor display or television set has heretofore been put into practice. In the image recording and reproducing system, a wide-screen image signal is recorded as a laterally (horizontally) spatially compressed signal by a magnetic recording and reproducing apparatus for recording an image signal of 4:3 aspect ratio. During reproduction, the horizontally spatially compressed image signal is reproduced from the magnetic recording and reproducing apparatus and is visually displayed as a wide-screen image on a wide-screen monitor in such a way that the horizontal scanning width thereof is enlarged. In accordance with the above-described arrangement, since an image signal having a normal aspect ratio of 4:3 also can be recorded and reproduced, it is possible to realize an apparatus capable of coping with both a normal-screen image signal and a wide-screen image signal.
As is known, in a video tape recorder conforming to an 8-mm video system, since the lower sideband of the frequency-modulated luminance signal of an image signal to be recorded influences an audio frequency-modulated signal and a low-converted chrominance signal as noise, there is provided a trap circuit for attenuating frequency components corresponding to the audio frequency-modulated signal and the low-converted chrominance signal in the lower sideband.
Conventionally, the circuit arrangement shown in FIG. 1, which has the effect of preventing an inverted white peak phenomenon from occurring in a reproduced image, is employed as a reproducing circuit for a magnetic recording and reproducing apparatus for frequency-modulating and recording an image signal (the luminance component thereof) on a magnetic tape in the manner used in, for example, the 8-mm video system. During recording, an image signal having a frequency distribution, such as that shown in FIG. 2(a), is converted into a signal having a frequency distribution, such as that shown in FIG. 2(b), by frequency modulation, and the thus-obtained signal is recorded on a magnetic tape.
In the reproducing circuit shown in FIG. 1, the signal (particularly, the frequency-modulated signal) recorded on a magnetic tape 40 is converted into an electrical signal by a magnetic head 42, and the output of the magnetic head 42 is amplified to a predetermined level by a head amplifier 44. The head amplifier 44 outputs a signal the high frequency band of which is attenuated according to the frequency characteristics of the magnetic tape 40, as shown in FIG. 2(c).
A soft limiter circuit 46 limits the amplitude of the output of the head amplifier 44 by approximately 10-12 dB, whereby a high frequency band component is restored as shown in FIG. 2(d). A high-frequency-band enhancing circuit 48, which has the amplification characteristic shown in FIG. 2(e), selectively enhances the high frequency band of the output of the soft limiter circuit 46. Thus, a reproduced signal is obtained in which the high frequency band is restored to the same level as the low frequency band, as shown in FIG. 2(f).
A hard limiter circuit 50 limits the amplitude of the output of the high-frequency-band enhancing circuit 48 by approximately 40-50 dB, and the output of the hard limiter circuit 50 is frequency-demodulated by a frequency demodulating circuit 52. Thus, the inverted white peak phenomenon is prevented.
A horizontally compressed image signal has an energy distribution in which the level of the image signal increases at high frequencies according to a compression ratio, as shown in FIG. 3. Accordingly, if the luminance signal of the horizontally compressed image signal is frequency-modulated, the energy components of the respective upper and lower sidebands increase as shown in FIG. 4, and the influence of the lower sideband on an audio frequency-modulated signal and a low-converted chrominance signal increases.
If the horizontally compressed wide-screen image signal is reproduced by the reproducing circuit shown in FIG. 1, it is impossible to achieve a satisfactory reproduction image quality; specifically, a high frequency band runs short compared to a low frequency band. This is because the recorded signal contains larger amounts of high-frequency-band components than a normal-screen image signal and, therefore, the wide-screen image signal differs from the normal-screen image signal in frequency distribution.
FIGS. 5(a) to 5(f) are views similar to FIGS. 2(a) to 2(f), but shows the characteristics of the wide-screen image signal. If a wide-screen image signal having large amounts of high-frequency components as shown in FIG. 5(a) is to be recorded or reproduced, the high-frequency-band enhancing circuit 48 for the normal-screen image signal, which has the characteristic shown in FIG. 2(e), is employed. As a result, a signal in which the high frequency band runs short compared to the low frequency band as shown in FIG. 5(f) is formed, so that it is impossible to achieve a satisfactory effect of preventing an inverted white peak phenomenon.
As is also known, in the case of the conventional image recording and reproducing apparatus, if both a normal-screen image signal (an image signal which is not horizontally compressed) and a wide-screen image signal (an image signal which is horizontally compressed) are recorded on one magnetic tape, an operator needs to determine whether an image signal which is being reproduced is the normal-screen image signal or the wide-screen image signal, on the basis of the shape of an image which is visually displayed. If a subject having a well-known shape is displayed, the operator can easily make such a decision. However, if a subject having an unknown shape is displayed, it is difficult for the operator to discriminate between the normal-screen image signal and the wide-screen image signal.
For example, if a perfectly round subject is reproduced as a wide-screen image signal, it is displayed as a perfect circle on a wide-screen monitor having an aspect ratio of 16:9, as shown in FIG. 6. However, in the case of a normal-screen monitor having an aspect ratio of 4:3, the subject is displayed as an ellipse which is vertically extended. In this case, an operator who knows that the original subject is perfectly round can easily determine that it is preferable to display the reproduced image on a screen of 16:9 aspect ratio. However, an operator who does not know that the original subject is round or elliptical can not determine which monitor screen is preferable.
Further, if the horizontal ratio of the image is adjusted in a reproducing apparatus and the subject is displayed at a correct ratio with the right and left portions of the image omitted as shown in FIG. 7 (side panel display), since the subject itself is displayed at a correct ratio, an operator does not have a sense of incompatibility and cannot know that the right and left portions of the image are omitted. For this reason, in an arrangement in which the right and left display positions can be adjusted (panning) according to the subject, it may be impossible to utilize such function.